Sheets and the like materials each carrying a sticking layer offer the advantage that they can be stuck to substrates with so-called "fingertip ease" but are deficient in bonding strength and resistance to slip stress because of the inherent nature of the sticking agent. On the other hand, sheets and other materials each carrying an adhesive layer insure permanent bonding to adherends but require not only subsequent drying or heating but also application of a pressure over a certain time period, thus being inferior in workability.
The foregoing suggests that if a stick-adhesive composition that would undergo spontaneous transition from a sticking agent to an adhesive agent after application to any adherend should ever be developed, both the demand for ease of application and the demand for permanent adhesion could be successfully reconciled and satisfied.
Much research has been undertaken into stick-adhesive agents. By way of illustration, Japanese Kokai Tokkyo Koho No. 63-10680 discloses a stick-adhesive composition comprising a monofunctional acrylic monomer, a compound containing two or more acryloyl groups, a compound containing two or more epoxy groups and a masked epoxy-curing agent.
Japanese Kokai Tokkyo Koho No. 51-6235 discloses a stick-adhesive composition comprising a mixture of n-butyl acrylate and 2-ethylhexyl acrylate, a functional vinyl monomer and a vinyl monomer copolymerizable therewith.
Furthermore, Japanese Kokai Tokkyo Koho No. 61-66631 describes a continuous lapping method for cladding a piece of furniture or an architectural member with a decorative sheet employing a stick-adhesive composition of the urethane prepolymer type which comprises paying out an endless decorative sheet from a roll, applying said stick-adhesive composition to the reverse side of said decorative sheet in the course of its travel, drying the same and applying the sheet to the furniture or architectural member through a roll set adapted to compress the sheet against said member in registry with the surface pattern of the latter. The stick-adhesive composition employed in this method develops a pressure-sticking property within 8 hours after evaporation of the coating solvent and, thereafter, an adhesive property as the curing reaction proceeds in line with progressive absorption of moisture with or without the aid of a curing component.
However, the stick-adhesive composition proposed in Japanese Kokai Tokkyo Koho No. 63-10680 has the disadvantage that heating is required for the conversion from a sticking agent to a bonding agent. The stick-adhesive composition described in Japanese Kokai Tokkyo Koho No. 51-6235 is also disadvantageous in that heat curing is required after application to the substrate. This need for a post-heating procedure for said conversion from a sticking agent to an adhesive agent is not only an economic deterrent because this requires additional work after application but a serious limiting factor in the utility of the composition because it cannot be utilized in applications where heat is abhorred or in the art of transfer printing sheets which are to remain on the substrates.
The stick-adhesive composition according to Japanese Kokai Tokkyo Koho No. 61-66631 is subject to a time limit that its pressure adhesivity is available only up to 8 hours after evaporation of the coating solvent. Moreover, it can never be used for transfer sheets which are marketed in the condition preformed with a stick-adhesive layer.
It is, therefore, an object of the present invention to provide a stick-adhesive composition with which a final product can be marketed as carrying a stick adhesive layer and applied to the substrate by simple pressing as it is the case with the conventional adhesive material and which provides a permanent bond as it is simply allowed to stand and undergo spontaneous transition from a sticking agent to an adhesive agent with the progress of time after application.
It is another object of the invention to provide a stick-adhesive layer formed from such stick-adhesive composition.
It is a further object of the invention to provide a transfer sheet having said stick-adhesive layer.